Gas-fueled heating apparatus



April 1, 1958 A. F. HOLDEN GAS-FUELED HEATING APPARATUS Filed Jan. 25, 1955' INVENTOR ARTEMAS F. HOLDEN I Z a 2 ATTORNEYS 2,828,813 GAS-FUELED HEATING APPARATUS Artemas F. Holden, Milford, Mich.

Application January 25, 1955, Serial No. 483,941

9 Claims. (Cl. 158-7) This invention relates to heating apparatus of the gasfired, porous wall type, wherein a combustible mixture of gas and air is passed through the furnace wall from one side to the other, and combustion takes place over a large area of the inner side of the furnace wall, heating the wall to incandescence.

in heating apparatus of the above-mentioned type, serious operating problems may arise from the tendency of the flame to creep outwardly through the porous refractory wall and cause back-fire or explosion of the combustible mixture on the outside surface of the wall. Such heat penetration and back-firing is primarily caused by excessive penetration of heat from the firewall surface outwardly through the furnace wall so as to ignite the combustible mixture within and finally at the outside surface of the porous wall.

The construction of the porous wall unit of the present invention differs from certain prior constructions in that the present construction promotes a uniform rate of flow of the combustible gas-air mixture inwardly through the porous refractory to the inside surface thereof. This is accomplished by providing a series of holes extending inwardly from the outside surface of the porous refractory wall and terminating at least an inch from the inner, firewall surface thereof. The incoming gas-air mixture is conducted through the passages and flows from the passages to the inside surface of the wall, the gas diffusing substantially uniformly through the inner zone of the wall and providing substantially uniform heating of the entire firewall surface. The incoming gas-air mixture extracts heat from the interior of the porous wall structure so as to maintain the wall sufficiently cool to prevent the flame from creeping outwardly through the wall and igniting the combustible gas-air mixture on the outside surface of the wall.

The best form in which I have contemplated applying my invention is illustrated in the accompanying drawings forming part of this specification, in which:

Fig. 1 is a perspective view of a furnace constructed according to the present invention.

Fig. 2 is a transverse section taken on the line 2, 2 of Fig. 1.

Fig. 3 is a longitudinal section of the furnace taken on the line 3, 3 of Fig. 1.

Fig. 4 is an enlarged transverse section of the furnace wall.

Referring now to the drawings, the furnace of the present invention has a jacketed or double-walled furnace shell 10, forming the outer walls of the furnace. The front wall 11 of the shell is provided with a rectangular central openings 12 for access to the interior of the furnace.

The shell 10 may be formed from steel plates welded together to form a series of jackets 14, a jacket lying along each wall of the furnace that is to be a luminous firewall. The plates forming the shell 10 may be from 10 gauge to of an inch in thickness, depending on the structural strength required. In the furnace shown,

jackets 14 extend only on the two sides, the top, the floor, and the back of the furnace, the front of the furnace being formed of a single plate lined with conventional refractory, as will be described. The welds joining together the plates forming the jackets 14 are continuous so as to prevent leakage of gas from the jackets along the joints. The jackets may be from one to two inches in thickness depending on the size of the furnace and the number of connections for introducing the combustible mixture of gases within the jackets.

One or more nipples 15 are providedon the exterior of the jackets 14 for introducing the combustible mixture of gases within the jackets. One or more nipples may be provided for each jacket 14, or the jackets may be interconnected and one nipple supply more than one or all of the jackets, the only requirement being that there must be substantially uniform pressure throughout the jackets during operation of the furnace.

The interior surface of the furnace shell 10 is lined with refractory ceramic material, such as individual firebrick or preformed slab.- The portions of the furnace walls that are to be luminous firewalls (in this instance the back, top, side and bottom walls of the furnace) are lined with insulating, lightweight firebrick; while the portions of the furnace walls which are not to be luminous firewalls (in this instance the front wall of the furnace) are lined with heavy firebrick or slabs. The heavy firebrick may be conventional in all respects, being selected from a fireclay that withstands the operating temperature of the furnace. The front wall is preferably about four and one-half inches in thickness.

The inner wall 16 of each jacket 14 of the furnace shell is provided with a series of holes 17 for passing combustible gases to the interior of the furnace, the holes 17 being located only on the walls that are to be luminous firewalls of the furnace. The holes 17 are spaced to give a sufficiently even distribution of combustible gases along the exterior surface of the refractory wall 19. I have found that one-inch holes spaced on four-and-one-half inch centers will provide sufficient distribution of the combustible gases.

The refractory walls 19 are formed of lightweight, insulating firebrick which may be in the form of standard size bricks 20, or in the form of a precast slab. The fire brick of which the. walls 19 are composed, is formed of refractory ceramic material consisting principally of silica and alumina and having a porosity of about 40% or greater. Bricks having a porosity up to about have been used successfully, the firebrick preferably being of the type'made from a mixture of fireclay and powdered or finely divided combustible material, such as wood dust, the combustible material subsequently being burned out in the calcined brick to provide a very lightweight, porous brick. Such bricks are well-known in the trade.

Each of the bricks 20 is drilled or otherwise formed to provide a series of holes or passages 21 extending from the outside of the brick a substantial distance through the brick towards the other'side. In the furnace shown, the bricks 20, of which the firewalls 19 are formed, are laid on edge to provide a refractory wall two and a half inches in thickness, the passages 21 leading from the outer towards the inner side of the refractory wall. I have found that a standard 2 /2" x 4%" x 9" brick, having two, three, or four half-inch holes drilled along the 2 /2 inch dimension halfway through the thickness of the brick or to Within about one to one-and-one-quarter inches of the inside face will provide sufficiently equal distribution of the combustible gases along the entire inner face of the walls 19 and also avoid back-firing at furnace temperatures in excess of 2000 F.

In forming each firewall 19 of the furnace, the bricks the 20 are set with high temperature refractory cement in the conventional way, the open ends of the passages 21 terminating against the inner walls 16 of the jackets 14, but no mortar being placed between the bricks and the walls. with the holes 17 in the inner wall 16 of the furnace shell since there will be sumcient room for passage of combustible gases between the outer surfaces of the firebrick walls and the inner walls '16 of the shell. The refractory cement must penetrate the bricks 2i sufficiently to provide a good bond and prevent any leakage of combustible gases through the joints, without filling the porous structure of the bricks excessively so as to interfere with flow of the gases through the bricks. In addition the refractory cement must expand and contract with the furnace wall to maintain the joints between the bricks 20 tight.

In operation of the above-described furnace, a combustible mixture of gases is supplied to the jackets 14 of the furnace shell ll through suitable connections to the nipples 15. The pressure maintained within the jackets may be in the neighborhood of four to ten inches of water column. Preferably there is some excess of gas to air in the combustible mixture over the theoretically explosive mixture of gases.

The combustible gases burn at the inner surface of the refractory firewalls l9, heating the surface of the firewalls to incandescence and providing a very intense, radiant heat. However, the insulating firebrick is a very poor conductor of heat and, in addition, the combustible gases fiowing inwardly to the inner surface of cool the interior of the firewalls, maintaining the outer surfaces of the firewalls at a relatively low temperature which is well below the ignition point of the gases, thus preventing backfire and explosion of the combustible gases within the jackets l4.

Such a furnace has an extremely high efiiciency and the walls of the furnace soak up very little heat, the furnace being capable of being heated and cooled down relatively rapidly, since only a relatively small volume of firebrick is substantially heated. A furnace of this type may be heated to an operating temperature of about 2809" P. in 2 /2 to minutes.

If it is desired that the furnace be operated by intermittent firing, or that the volume of combustible gases being passed to the jackets 14 be substantially reduced, it is preferable to use a refractory wall that may be as much as 9 inches in thickness. In such event, it may be desirable to have the holes 21 terminate a greater distance from the inner surface of the refractory wall so that the firing may be stopped altogether from time to time without hazard of the heat of the furnace being conducted through the refractory wall so as to cause a back-fire or explosion.

The furnace of the present invention may be shut down by first shutting off the gaseous fuel, but continuing the supply of air to the furnace until the inner face of the refractory firewall 19 has become sufficiently cooled by passage of air therethrough. Otherwise, there is some hazard of the entire refractory structure of the furnace becoming heated throughout, which might result in warpage of the steel furnace shell 10. However, it if is desired that the furnace be held in standby condition for a period without excessive cooling of the furnace, the gaseous fuel supply may be shut ofi, and air being supplied to the jackets 14. 'However, to avoid cooling the interior of the furnace, the air may be circulated through the jackets and released rather than forced through the refractory wall, as by opening an exhaust valve (not shown) in the jackets to provide a current of air flowing through the jackets for cooling the outer surface only of the refractory wall 2%.

In the porous firewall above described, the principal flow of combustible gases through the wall is through the passages 21 and then diverging from the inner ends of those passages to the inside surface of the wall. Since the total cross-sectional area of the passages 21 is a relatively small part of the total wall area (only about 2% The passages 21 in the bricks need not coincide 4 in the preferred example) the gas enters the refractory Wall at a relatively high velocity, exercising the greatest cooling effect in the refractory beyond the ends of the passages. In order to obtain the necessary cooling effect, the total area of the passages 21 should not exceed about 5% of the total surface area of the firewall.

The furnace wall construction of this application is of general applicability to furnaces of various types and for various purposes wherein a firewall furnace construction is advantageous.

I claim:

1. A porous firewall for a luminous radiant firing furnace, comprising a wall of lightweight, insulating firebrick having a porosity of over 40% and a thickness of at least 2 /2 inches, the firing surface of said wall being generally continuous, and the other surface of said wall having a plurality of more or less regularly spaced relatively unrestricted gas distributing holes extending part way and at least halfway through said wall, said holes having a size such as to conduct a gas mixture at substantially unreduced inlet face pressure to the end of said holes, said holes having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of the holes being a small minor proportion of the total area of the wall, and a jacket for receiving the combustible mixture of gases, said jacket extending along said other surface of said firewall and having gas distributing means adjacent said firewall.

2. A porous firewall for a luminous radiant firing furnace, comprising a wall of lightweight, insulating firebrick having a porosity within the range of 40SO% and a thickness of at least 2 /2 inches, the firing surface of said wall being generally continuous, and the other surface of said wall having a plurality of more or less regularly spaced relatively unrestricted gas distributing holes extending at least halfway through said wall to terminate at least one inch short of the firing surface, said holes having a size such as to conduct a gas mixture at substantially unreduced inlet face pressure to the end of said holes, said holes having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of the holes being a small minor proportion of the total area of the wall, and a jacket for receiving the combustible mixture of gases, said jacket extending along said other surface of said firewall and having gas distributing means adjacent said firewall.

3. A gas-fired furnace, said furnace comprising a ferrous metal furnace shell, at least some of the sides of which are formed of two spaced-plates forming a jacket, the furnace shell having a lining of refractory material and the refractory material adjacent the jackets being porous andhavinga thickness of at least 2 /2 inches, the outer surface of said lining having a plurality of regularly spaced relatively unrestricted gas distributing holes extending at least halfway therethrough, said holes having a size such as to conduct a gas mixture at substantially unreduced inlet face pressure to the end of said holes, said holes having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said fire 2 /2 inches and having a porosity of at least 40%, the outer surface of said lining having a plurality of regularly spaced relatively unrestricted gas distributing holes extending at least halfway through to within not less than approximately one inch of the inner surface of the wall, said holes having a size such as to conduct a gas mixture at substantially unreduced inlet face pressure to the end of said holes, said holes having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of the holes being a small minor proportion of the total area of each wall, and the jacket having gas distributing means communicating the interior of the jacket with the outer surface of said wall.

5. A gas-fired furnace, said furnace comprising a ferrous metal furnace shell, at least some of the sides of which are formed of two spaced plates forming a jacket, the furnace shell having a lining of refractory material and the refractory material adjacent the jackets being lightweight insulating firebrick forming a wall having a thickness in the order of 2 /2 inches or more and having a porosity of at least 40%, the outer surface of said wall having a plurality of more or less regularly spaced relatively unrestricted gas distributing holes extending at least halfway through to within not less than approximately one inch from the inner surface of the wall, said holes having a size such as to conduct a gas mixture at substantially unreduced inlet face pressure to the end of said holes, said holes having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of the holes being not in excess of 5% of the total area of each wall, and the jacket having gas distributing means communicating the interior of the jacket with the outer surface of said wall.

6. A porous firewall for a luminous radiant firing furnace, comprising a wall of lightweight insulating firebrick having a porosity within the range of 4080% and a thickness of at least 2 /2 inches, the inside surface of said wall being generally continuous and the outside surface of said wall having a plurality of spaced substantially unrestricted gas distributing passages extending through a major proportion of the wall thickness to within not less than approximately one inch of the inside surface of said wall, said passages having a size such as to conduct a gas mixture at substantiallly unreduced inlet face pressure to the end of said passages, said passages having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of the passages being a small minor proportion of the total area of the wall.

7. A porous firewall for a luminous radiant firing furnace, comprising a wall of refractory ceramic material having a porosity of over 40% and a thickness of at least 2 /2 inches, the firing surface of said wall being generally continuous and the other surface of said wall having a plurality of relatively unrestricted gas distributing inlet passages extending through major proportion of said thickness to within not less than approximately one inch of said firing surface, said passages having a size such as to conduct a gas mixture at substantially unreduced inlet face pressure to the end of said pasages, said passages having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of the passages comprising not more than 5% of the total area of the wall.

8. A porous refractory gas firewall through which a combustible gas mixture flows under a predetermined pressure head to ignite and burn at a firing face of predetermined operating temperature on the low pressure side of said wall, characterized by a plurality of relatively unrestricted gas distribution passages extending from the face of said wall on the high pressure side part way in the order of one-half way or more through said wall toward said firing face, said passages having a size such as to conduct said gas mixture at substantially unreduced inlet face pressure to the end of said passages, said passages having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, the total cross-sectional area of said passages constituting a small minor proportion of the total area of said wall, the thickness ofsaid wall being in the order of 2 /2 inches or more and adequate to provide a temperature gradient from the operating temperature of said firing face to a temperature below the ignition temperature of said combustible gas mixture.

9. A porous refractory firewall through which a combustible gas mixture flows for ignition and burning at one face of the wall characterized by means for increasing the gas flow at a given pressure head through a wall area of given thickness in the order of 2 /2 inches or more comprising a plurality of relatively unrestricted gas distribution passages extending part way in the order of onehalf way or more through said wall toward said one face thereof, said passages having a size such as to conduct said gas mixture at substantially unreduced inlet face pressure to the end of said passages, said passages having a spacing pattern relative to the remaining wall thickness such as to provide required uniformity of gas mixture distribution over the firing face of said firewall, and the total cross sectional area of said passages being a small minor proportion of said wall area.

References Cited in the file of this patent UNITED STATES PATENTS 1,074,110 Fyfe Sept. 30, '1913 1,223,308 Bone et a1. Apr. 17, 1917 1,304,755 Ellis May 27, 1919 2,194,208 Moran Mar. 19, 1940 2,311,350 Richardson Feb. 16, 1943 

